1. Field of the Invention
The present invention relates to a method for writing data to a flash memory, and particularly to a method for writing data to a flash memory while balancing wear of the flash memory.
2. Background of the Invention
Currently, personal portable electronic products generally employ two means to store data: one is a random access memory (RAM), and the other is a flash memory. The RAM is relatively cheap, and has fast access rates. However, the RAM must work with a power supply in order to store data. If the power supply is shut off, data stored in the RAM is lost. At present, there are no personal portable electronic products that can provide a 24-hour power supply. Thus the RAM is not suitable for storing important data.
The flash memory is a kind of non-volatile memory (NVM). It has highly integrated components, and can protect data under conditions of no power supply. However, if the flash memory is performing an operation (such as writing or deleting) on data stored on a sector thereof while the power supply is shut off, data originally stored on the sector is prone to be lost. In addition, if the flash memory employs a File Allocation Table (FAT) file system, and the flash memory is simply updating a file allocation table or a ROOT table thereof when the power supply is shut off, all data on the flash memory is lost.
China Patent Application No. 01119887.7, published on Jan. 29, 2003, discloses a flash file management method. The invention treats each physical sector of a flash memory as a management unit that has a file head control information area, a data area, and a file status information area. Each file is made up of one or more management units. When a file is stored or modified, data on the file is stored in a void management unit. Then original management units concerned with the file are deleted, and the file allocation table in a RAM is modified accordingly.
The above-mentioned invention provides a stable flash file management method, and can minimize the risk of data loss when the power supply of the flash memory is shut off. However, the invention does not balance wear among the management units. That is, some of the physical sectors of the flash memory are used more frequently than others. The more frequently used physical sectors are prone to sustain the most wear and reach the end of their working lifetimes prematurely. This eventually leads to reduced capacity of the flash memory. Therefore, a method for balancing wear among the management units is needed to improve the useful working lifetime of the flash memory.